Low friction loss automatic transmission

Abstract

An automatic transmission including a double pinion planetary gear unit PG 1 , two single pinion planetary gear units PG 2 and PG 3 and six frictional elements (viz., six clutches) C 1 to C 6 is so constructed as to establish nine forward speeds and one reverse speed by simultaneously putting selected three of the six frictional elements C 1 to C 6 into their engaged condition. The frictional elements C 1 to C 6 are of a type including mutually rotatable friction plates that cause production of an oil dragging resistance when the frictional element is under idling condition. With the simultaneously engaged condition of the three frictional elements, each speed is established with a reduced friction loss of the automatic transmission.

What is claimed is: 
     
       1. An automatic transmission comprising:
 input and output shafts; 
 a first planetary gear unit of double pinion type, that includes a first sun gear, a first ring gear and a first carrier that carries first double pinions that mesh with both the first sun gear and the first ring; 
 a second planetary gear unit of single pinion type, that includes a second sun gear, a second ring gear and a second carrier that carries second single pinions that mesh with both the second sun gear and the second ring gear; 
 a third planetary gear unit of single pinion type, that includes a third sun gear, a third ring gear and a third carrier that carries third single pinions that mesh with both the third sun gear and the third ring gear; and 
 six frictional elements, each frictional element including mutually rotatable friction plates that cause production of an oil dragging resistance when the friction element is under idling condition, 
 wherein by selectively engaging and disengaging the six frictional elements, a torque of the input shaft is transmitted to the output shaft while making a rotation speed change therebetween to establish at least eight forward speeds, 
 wherein the output shaft is constantly connected to the third carrier, the first ring gear is constantly connected to a first fixing member to be fixed, the first carrier and the second sun gear are constantly connected to constitute a first rotatable member, the first sun gear and the third ring gear are constantly connected to constitute a second rotatable member, and 
 wherein the six frictional elements are a first frictional element that selectively connects the second carrier and the second rotatable member, a second frictional member that selectively connects the second carrier and the first rotatable member, a third frictional member that selectively connects the second ring gear and the third sun gear, a fourth frictional element that selectively connects the input shaft and the third sun gear, a fifth frictional element that selectively connects the second ring gear and the third carrier and a sixth frictional element that selectively connects the input shaft and the second carrier; and wherein by simultaneously putting selected three of the six frictional elements into their engaged condition, at least eight forward speeds and one reverse speed are established. 
 
     
     
       2. An automatic transmission as claimed in  claim 1 , in which by simultaneously putting selected three of the six frictional elements into their engaged condition, nine forward speeds are established, in which:
 a first forward speed is established by simultaneously putting second, fourth and fifth frictional elements into their engaged condition; 
 a second forward speed is established by simultaneously putting first, second and fourth frictional elements into their engaged condition; 
 a third forward speed is established by simultaneously putting first, fourth and fifth frictional elements into their engaged condition; 
 a fourth forward speed is established by simultaneously putting first, third and fourth frictional elements into their engaged condition; 
 a fifth forward speed is established by simultaneously putting first, fourth and sixth frictional elements into their engaged condition; 
 a sixth forward speed is established by simultaneously putting first, third and sixth frictional elements into their engaged condition; 
 a seventh forward speed is established by simultaneously putting first, fifth and sixth frictional elements into their engaged condition; 
 an eighth forward speed is established by simultaneously putting third, fifth and sixth frictional elements into their engaged condition; and 
 a ninth forward speed is established by simultaneously putting fourth, fifth and sixth frictional elements into their engaged condition. 
 
     
     
       3. An automatic transmission as claimed in  claim 1 , in which:
 the reverse speed is established by simultaneously putting second, fourth and sixth frictional elements into their engaged condition. 
 
     
     
       4. An automatic transmission as claimed in  claim 1 ,
 in which the six frictional elements are all clutches.